This invention relates to a device for attaching rollers to a carriage adapted to move in sliding motion along a rail in a drawing apparatus, plotting machine or like apparatus of the rail type.
In mounting a carriage for sliding motion on a rail in a drawing apparatus or a plotting machine of the rail type, the usual practice is to bring a plurality of rollers each rotatably attached to the carriage through a shaft into engagement with at least a pair of rail surfaces disposed parallel to each other and extending along the longitudinal axis of the rail, and the movement of the carriage along the rail is controlled by the rail surfaces.
In the aforementioned construction of the prior art, when a force oriented longitudinally of the rail is exerted on the carriage, the rollers rotate on the respective rail surfaces while being maintained in intimate engagement therewith, and the carriage is capable of accurately moving longitudinally of the rail without moving toward and away from the rail surfaces at right angles thereto because such wobbling movements are precluded by the rail surfaces. However, technical difficulty is experienced in accurately maintaining the rollers in intimate with the rail surfaces. That is, care should be taken in accurately attaching the rollers to the carriage and in forming the rail surfaces on the rail. Moreover, these parts should be machined to a high degree of precision. This has made it impossible to replace the old carriage by a new one and the old carriage and the rail must be replaced as a unit by a new set of a carriage and rail. This is a drawback which causes inconvenience.
If the rollers press against the respective rail surfaces with a high force when the carriage is slidably mounted on the rail, the movement of the carriage along the rail will be obstructed and smooth movement of the carriage cannot be expected. If, on the other hand, the surfaces of the rollers are spaced apart, even if slightly, from the rail surfaces, the carriage will become wobbly when moving along the rail.
In assembling a drawing apparatus or a plotting machine of the rail type, after the carriage has been slidably mounted on the rail and adjustments have been effected such that the rollers are maintained in engagement with the respective rail surfaces with precision and accuracy, difficulty is experienced in effecting readjustments of the position of each of the rollers against the rail surfaces if the rollers are detached from the rail. Thus, in transporting a drawing apparatus or plotting machine of the rail type by disassembling it, it is necessary to pack the carriage and the rail as a unit without removing the carriage from the rail. This has the disadvantage of the package becoming too large to handle. Moreover, there is the trouble of providing carriage movement precluding means in order to prevent movement of the carriage along the rail during transportation.
In order to obviate the aforementioned disadvantages of the prior art, proposals have been made to use spring means for urging a roller by the biasing force thereof to move toward the respective rail surface by supporting the roller such that it can be moved toward or away from the rail surface. This arrangement has a disadvantage in that the rollers can be brought into engagement with the respective rail surfaces with precision and accuracy even if there is an error in the positions of the rollers relative to the rail. However, application of high pressure to any one of the rollers in a direction which is opposite to the direction in which it is moved by the biasing force of the spring means causes the roller to move in a wrong direction against the biasing force of the spring means. Thus, it becomes impossible for the carriage to move accurately along the longitudinal axis of the rail because it deviates therefrom in its movement. This disadvantage can best be obviated by providing means whereby the rollers can be made impervious to any force which would be exerted thereon and would tend to move the same in a direction opposite to the direction in which it is urged to move by the biasing force of the spring means. According to the invention, there is provided a device which make it possible to attain this end.